A power source circuit including a direct current (DC) to DC converter that includes a coil and a switching element has been proposed in conventional technology (Patent Literature 1). Such power source circuits can be used as lighting circuits to supply power to light sources.
The power source circuit disclosed in Patent Literature 1 includes a rectifying and smoothing circuit, a transformer, a switching element, a control circuit, a diode, and a capacitor. The rectifying and smoothing circuit rectifies and smoothes AC current supplied from an AC power source, and then outputs the current. The transformer includes a power source side coil and a load side coil magnetically connected to the source side coil. One end of the power source side coil is connected to the high potential side of the rectifying and smoothing circuit. The switching element is connected to the other end of the power source side coil. The control circuit carries out on and off control of the switching element. The diode and the capacitor are for rectifying and smoothing a voltage induced at the load side coil, and supplying the voltage to a load such as a light source.
This lighting circuit further includes a voltage supply coil that is magnetically connected to the power source side coil. The voltage supply coil is for supplying a driving voltage to a power source terminal of the control circuit.